Recent studies have shown that several metal ions inhibit plaque formation and reduce the acidogenicity of dental plaque. The aim of the present study is to compare the effect on plaque and gingivitis of 2.2 mM CuSO4 with an equimolar solution of chlorhexidine in a modified experimental gingivitis model. The study will be performed according to a double-blind crossover design. Before each experimental period the GI will be recorded and the participants' teeth scaled and polished to remove all supragingival deposits. All mechanical oral hygiene will be suspended during the experimental periods.